Driving assistance device and driving assistance method

ABSTRACT

An ECU as a driving assistance device has a traffic sign detection section, a lane entry detection section and a judgment section. The traffic sign detection section detects traffic signs including a speed limit symbol based on front-image data captured by an in-vehicle camera. The lane entry detection section detects that the own vehicle has entered a ramp lane to leave a highway. The judgment section detects an extent of a current driving lane as the ramp lane when following conditions (c1) and (c2) are satisfied after the lane entry detection section detects the entry of the own vehicle into the ramp lane: (c1) not less than two traffic signs are arranged along the current driving lane in forward direction of the vehicle; and (c2) an arrangement of speed limit symbols included in the detected traffic signs satisfy a predetermined speed reduction pattern.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to and claims priority from Japanese PatentApplication No. 2015-110569 filed on May 29, 2015, the contents of whichare hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to driving assistance devices and methodscapable of detecting and assisting travel of a vehicle on a connectionlane, i.e. a ramp lane connected to a driving lane on a highway, throughwhich the vehicle leaves the highway.

2. Description of the Related Art

Recently, there have been proposed driving assistance devices capable ofperforming driving assistance for the driver of a vehicle. For example,a conventional driving assistance device detects a ramp lane as aconnection lane connected to a driving lane on a highway (vehicleroadway), through which the vehicle leaves the highway.

A patent document, Japanese patent laid open publication No. JP2008-189093 discloses a conventional vehicle driving control devicecapable of detecting the presence of a ramp lane, i.e. a connection laneconnected to a driving lane on a highway, on the basis of navigationinformation transmitted from a vehicle navigation system mounted on thevehicle. The vehicle driving control device detects entry of the ownvehicle into a ramp lane as a connection lane connected to a drivinglane on a highway when:

(a) detecting the presence of a ramp lane;

(b) detecting or estimating occurrence of a driver's request to change acurrent driving lane on a highway; and

(c) detecting that the own vehicle crosses a dotted lane boundary linewhich divides the current driving lane from the ramp lane.

The conventional vehicle driving control device detects that the ownvehicle has passed through a connection lane when detecting that the ownvehicle has passed through a tollgate or is running on a general roadwayor a parking space such as a highway rest stop on the basis ofnavigation information transmitted from the vehicle navigation system.

However, because the conventional vehicle driving control devicedisclosed in the patent document previously described detects a place ofexit of the ramp lane as a connection lane on the basis of thenavigation information transmitted from the vehicle navigation device,if no vehicle navigation system is mounted on a vehicle, it isimpossible to apply the vehicle driving control device to the vehicle,and difficult for the driver of the vehicle to correctly detect a placeof exit of the ramp lane, i.e. detect whether or not the own vehicle haspassed the ramp lane, i.e. passed through the exit of the ramp lane.

SUMMARY

It is therefore desired to provide a driving assistance device capableof correctly detecting completion of driving on a connection lane, i.e.a ramp lane connected to a driving lane on a highway without usingnavigation information provided from a navigation system.

An exemplary embodiment provides a driving assistance device having atraffic sign detection section, a lane entry detection section and ajudgment section. The traffic sign detection section detects trafficsigns on a basis of front image data captured by an in-vehicle cameramounted on an own vehicle. Each traffic sign includes at least a speedlimit symbol. The lane entry detection section detects that the ownvehicle enters a connection lane such as a ramp lane through which theown vehicle leaves a highway. The judgment section detects that acurrent driving lane, on which the own vehicle travels, is theconnection lane when the following conditions (c1) and (c2) aresatisfied after the lane entry detection section detects the entry ofthe own vehicle into the connection lane: (c1) the traffic signdetection section detects not less than two traffic signs which arearranged along the current driving lane in forward direction of the ownvehicle, and (c2) an arrangement of speed limit symbols included in thetraffic signs detected by the traffic sign detection section in theforward direction of the own vehicle satisfy a predetermined speedreduction pattern.

The driving assistance device according to the present invention detectstraffic signs including ramp signs on the basis of front images capturedby and transmitted from the in-vehicle camera. Each of the detectedtraffic signs includes at least a speed limit symbol. The drivingassistance device detects the entry of the own vehicle into a connectionlane such as a ramp lane. That is, the own vehicle can leave a highwaythrough the connection lane. Under the state in which the entry of theown vehicle into the connection lane has been detected, the drivingassistance device detects that a current driving lane is the connectionlane, i.e. the ramp lane when the following two conditions (c1) and (c2)are satisfied. (c1) When the traffic sign detection section has detectednot less than two traffic signs arranged along the current driving lanein forward direction of the own vehicle, and (c2) an arrangement ofspeed limit symbols included in the traffic signs detected by thetraffic sign detection section in the forward direction of the ownvehicle satisfy a predetermined speed reduction pattern.

In general, on the connection lane in the forward direction of avehicle, not less than two traffic signs, i.e. ramp signs including aspeed limit symbol are arranged at relatively narrow intervals. Thevehicle can leave a highway through the connection lane, i.e. the ramplane, and reduce its vehicle speed on the connection lane according tothe specific speed reduction pattern indicated by the speed limitsymbols included in the traffic signs which have been arranged on theconnection lane. Accordingly, it is possible for the driving assistancedevice to distinguish the connection lane from driving lanes on highwaysand general roadways, and correctly detect the presence of theconnection lane on the basis of the speed reduction pattern of the speedlimit symbols in the detected traffic signs such as ramp signs. It istherefore possible for the driving assistance device to detect the placeof the exit of the connection lane without using navigation information.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred, non-limiting embodiment of the present invention will bedescribed by way of example with reference to the accompanying drawings,in which:

FIG. 1 is a view showing a schematic structure of an ECU 20 as a drivingassistance device, various detection devices and sensors mounted on anown vehicle 50 according to an exemplary embodiment of the presentinvention;

FIG. 2 is a view showing a highway having multiple lanes Wh1, Wh2 andWh3 and a ramp lane Wr as connection lane, on which the own vehicle 50travels, and showing traffic signs as ramp signs Sg1, Sg2, Sg3 and Sg4arranged along the ramp lane Wr branched from a driving lane Wh1 on thehighway;

FIG. 3A is a view showing the speed limit symbol Sa1 of 90 km and theauxiliary symbol Sb (down arrow symbol) included in the ramp sign Sg1located at the entrance of the ramp lane Wr, displayed on the displayunit 31;

FIG. 3B is a view showing the speed limit symbol Sa2 of 70 km includedin the ramp sign Sg2 and the auxiliary symbol Sb (down arrow symbol),displayed on the display unit 31;

FIG. 3C is a view showing the speed limit symbol Sa3 of 50 km includedin the ramp sign Sg3 and the auxiliary symbol Sb (the down arrowsymbol), displayed on the display unit 31;

FIG. 3D is a view showing the speed limit symbol Sa4 of 30 km includedin the ramp sign Sg4, displayed on the display unit 31;

FIG. 4 is a flow chart showing a process of detecting a driving state ofthe own vehicle 50 on the ramp lane Wr, and notifying the detected stateto the driver of the own vehicle 50 through the display unit 31, etc.;and

FIG. 5 is a flow chart showing a process of detecting entry of the ownvehicle into the ramp lane Wr.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, various embodiments of the present invention will bedescribed with reference to the accompanying drawings. In the followingdescription of the various embodiments, like reference characters ornumerals designate like or equivalent component parts throughout theseveral diagrams.

EXEMPLARY EMBODIMENT

A description will be given of a driving assistance device 20 accordingto an exemplary embodiment with reference to FIG. 1 to FIG. 4.

The driving assistance device 20 according to the exemplary embodimentis mounted on a motor vehicle (hereinafter, the own vehicle 50). Thedriving assistance device 20 shown in FIG. 1 detects whether or not theown vehicle 50 enters a connection lane, for example, a ramp lane Wrshown in FIG. 2, which is connected to a current driving lane Wh1 on ahighway or a freeway on which the own vehicle 50 travels. The drivingassistance device 20 performs the driving assistance for the driver ofthe own vehicle 50.

In the following description, the driving assistance device 20 performsthe driving assist when the own vehicle 50 is running on the currentdriving lane on the highway, and enters the ramp lane Wr connected tothe current driving lane Wh1 on the highway. As shown in FIG. 2, theramp lane Wr is arranged at the most right side of the highway.

It is also possible to apply the driving assistance device 20 accordingto the exemplary embodiment to vehicles used in various countries havingdifferent traffic rules. For example, the driving assistance device 20according to the exemplary embodiment can perform the driving assistancewhen a vehicle enters a ramp lane which is located at a left side of ahighway.

A description will now be given of a schematic structure of the drivingassistance device 20 according to the exemplary embodiment withreference to FIG. 1.

FIG. 1 is a view showing a schematic structure of the driving assistancedevice 20, various detection devices and sensors mounted on an ownvehicle 50 according to the exemplary embodiment. As shown in FIG. 1,the driving assistance device 20 according to the exemplary embodimentis an electronic control device (hereinafter, the ECU 20). One or morein-vehicle cameras 10 capture image around the own vehicle 50, andtransmits image information regarding the captured image data to the ECU20. A turn signal indicator unit 11 lights and transmits a turn signalto the ECU 20. The ECU 20 receives the front image informationtransmitted from the in-vehicle camera 10 and the turn signaltransmitted from the turn signal indicator unit 11. The ECU 20 generatesand transmits driving information regarding the driving state and theramp lane to a display unit 31 as one of notification units.

The in-vehicle camera 10 is a monocular camera or a stereo cameracomposed of a charge coupled device (CCD) image sensor, a complementarymetal oxide semiconductor (CMOS) image sensor, a near infrared rayssensor, etc. For example, the in-vehicle camera 10 is mounted at anupper side of a windshield (or a wind screen) of the own vehicle 50. Thein-vehicle camera 10 captures front images within a predetermined anglerange in front of the own vehicle 50, and sequentially transmitscaptured front image data to the ECU 20.

The driver of the own vehicle 50 operates the turn signal indicator unit11 to indicate the direction of turning right or left of the own vehicle50. The turn signal indicator unit 11 transmits a turning instructionsignal to the ECU 20.

The ECU 20 is composed of a central processing unit (CPU), a read onlymemory (ROM), a random access memory (RAM), an input output interface(I/O interface), etc. The ROM stores various types of control programsin advance. The ECU 20 reads and executes the control programs stored inthe ROM, for example. The execution of the programs realizes thefunctions of a traffic sign detection section 21, a distance detectionsection 22, a driver's intention detection section 23, a lane entrydetection section 24, a notification control section 25 and a judgmentsection 26.

The traffic sign detection section 21 detects various types of trafficsigns, for example, the presence of each of the ramp signs Sg1, Sg2, Sg3and SG4 as traffic signs on the basis of front image data captured byand transmitted from the in-vehicle camera 10. The ramp signs Sg1, Sg2,Sg3 and Sg4 include at least speed limit symbols Sa1, Sa2, Sa3 and Sa4,respectively.

FIG. 2 is a view showing the highway having the multiple lanes Wh1, Wh2and Wh3 and the ramp lane Wr, on which the own vehicle 50 travels. Theramp lane Wr is a connection lane arranged between the highway and ageneral roadway. FIG. 2 shows traffic signs, i.e. the ramp signs Sg1,Sg2, Sg3 and Sg4 installed and arranged along the ramp lane Wr. The ramplane Wr is branched from the driving lane Wh1 on the highway. That is,FIG. 2 shows an example of right-side traveling on a highway in Europe.The highway has the three driving lanes Wh1, Wh2 and Wh3 on each side.As shown in FIG. 2, the ramp lane Wr is arranged along the driving laneWh1 located at the most right side in the forward direction of thehighway.

The ramp lane Wr is connected to the driving lane Wh1 on the highway atthe right side thereof through which the own vehicle 50 leaves thehighway. FIG. 2 shows the traffic signs, i.e. the ramp signs Sg1, Sg2,Sg3 and Sg4 located at the right side of the ramp lane Wr. The ownvehicle 50 passes through the ramp sign Sg1 installed at the entrance ofthe ramp lane Wr to leave the highway. In general, the ramp sign Sg1 isnot installed on each of the driving lanes Wh1, Wh2, Wh3 on the highwayas well as on a general road. Accordingly, when detecting the specifictraffic sign, i.e. the ramp sign Sg1, the ECU 20 as the drivingassistance device can detect the presence of the ramp lane Wr. FIG. 2shows the four ramp signs Sg1, Sg2, Sg3 and Sg4 located at the rightside of the ramp lane Wr when the own vehicle 50 travels on the ramplane Wr. However, actual ramp signs Sg1, Sg2, Sg3 and Sg4 are located toface the driver of the own vehicle 50 when the own vehicle 50 is runningon the ramp lane WR so that the driver of the own vehicle 50sequentially recognizes each of the ramp signs Sg1, Sg2, Sg3 and Sg4 infront of the own vehicle 50.

As shown in FIG. 2, the specific traffic sign, i.e. the ramp sign Sg1installed at the entrance of the ramp lane Wr includes a speed limitsymbol Sa1 and an auxiliary sign Sb (down arrow symbol) to provide anindication of a place where the own vehicle 50 leaves the highway. Thespeed limit symbol indicates an allowed speed limit of the own vehicle50 on the ramp lane Wr. The auxiliary sign Sb shows a down arrow sign asthe exit marker or symbol. The auxiliary sign Sb indicates a lower rightdirection when the driver of the own vehicle 50 views it from the frontside. Accordingly, when the own vehicle 50 goes to the right side on thebasis of the auxiliary sign Sb of the ramp sign Sg1, the own vehicle 50can leave the highway.

In general, ramp signs such as the ramp sign Sg1 are not located on thedriving lanes Wh1, Wh2, Wh3 of the highway and also on a generalroadway. For this reason, when detecting the ramp sign Sg1, the ECU 20as the driving assistance device can detect the presence of the ramplane Wr. Although FIG. 2 shows the three ramp signs Sg installed at theright side of the ramp lane Wr in the forward direction of the ownvehicle 50, there are in general various traffic signs as ramp signslocated along the shoulder of a ramp lane. For example, one ramp signincludes a speed limit symbol and a down arrow symbol (exit symbol), andother ramp signs include only speed limit symbols, respectively.

As shown in FIG. 2, the ramp sign Sg1 includes the speed limit symbolSa1 and the down arrow sign Sb. On the other hand, each of the rampsigns Sg2, Sg3 and Sg4 includes only the speed limit symbol Sa2, Sa3,and Sa4, respectively.

The traffic sign detection section 21 performs known pattern matching onthe basis of the front image data captured by and transmitted from thein-vehicle camera 10, and detects the ramp signs Sg1 including the speedlimit symbol and the down arrow symbol, and the ramp signs Sg2 to Sg4including a speed limit symbol only.

Various countries use a different exit symbol as one of the auxiliarysymbols included in the ramp sign Sg, which provides an indication of aplace where the own vehicle 50 may leave the driving lane on thehighway. For example, Japan uses a ramp sign Sg including the word“EXIT” which shows the exit from a highway. The traffic sign detectionsection 21 performs pattern matching of front image data captured by thein-vehicle camera 10 by using pattern data which correspond to thepredetermined country or various countries in which the own vehicletravels. The traffic sign detection section 21 detects a traffic sign asthe ramp sign Sg including a speed limit symbol Sa1, Sa2, Sa3 or Sa4 onthe basis of the results of the pattern matching and the front imagedata. FIG. 2 shows the four traffic signs Sg1 to Sg4, i.e. the ramp signSg1 including the ramp speed limit Sa1 of 90 km and the down arrow signSb, the ramp sign Sg2 including the ramp speed limit Sa2 of 70 Km, theramp sign Sg3 including the ramp speed limit Sa3 of 50 Km, and the rampsign Sg4 including the ramp speed limit Sa4 of 30 Km. In general, thenumber of the traffic signs as the ramp signs is changed on the basis ofa distance of the section, i.e. a length of the ramp lane Wr, etc.

The distance detection section 22 detects a distance Le in a widthdirection of the highway between the own vehicle 50 and the detectedtraffic sign, i.e. the ramp sign Sg1 detected by the traffic signdetection section 21. In more detail, the distance detection section 22detects the distance Le between the side surface of the own vehicle 50and the ramp sign Sg1 on the basis of the front image data captured bythe in-vehicle camera 10. It is also acceptable to use another distancebetween the detected traffic sign, i.e. the ramp sign Sg1 and the centerof the own vehicle in a width direction of the driving lanes Wh1, Wh2 orWh3 on the highway, or between the ramp sign Sg1 and the side surface ofthe own vehicle 50 on the current driving lane.

The driver's intention detection section 23 detects a driver's intentionfor the own vehicle 50 to change the current driving lane on the highwayon which the own vehicle 50 travels. In more detail, the driver's intenddetection section 23 detects the driver's intention for the own vehicle50, i.e., whether or not the driver of the own vehicle 50 intends tochange the driving lane on the highway and a change direction on thebasis of the turning instruction signal transmitted from the turn signalindicator unit 11.

The lane entry detection section 24 detects entry of the own vehicle 50into the ramp lane Wr, i.e. the connection lane connected between thehighway and a general road. In more detail, the lane entry detectionsection 24 detects that the own vehicle 50 has entered the ramp lane Wrwhen the following four conditions (1) to (4) are satisfied:

(1) the traffic sign detection section 21 detects the presence of atleast one ramp sign;(2) the distance Le detected by the distance detection section 22 isshorter than a predetermined distance Y (m);(3) the driver's intention detection section 23 detects that the driverintends changing the traveling direction of the own vehicle 50 towardthe ramp sign Sg1 corresponding to the forward direction of the ownvehicle 50; and(4) the speed of the own vehicle 50 which has entered the ramp lane Wris greater than a predetermined speed limit X.

The predetermined distance Y (m) used in the condition (2) has beendetermined on the basis of the road width of the driving lane on thehighway and the road width of the ramp lane. In more detail, thepredetermined distance Y (m) used in the condition (2) is determined onthe basis of the lane width of the driving lane on the highway adjacentto the ramp lane Wr, and a distance between a lane shoulder of theoutermost driving lane on the highway and the ramp sign Sg. For example,the predetermined distance Y (m) used in the condition (2) isapproximately 7 m which is a total distance of:

the lane width of the driving lane Wh1 (see FIG. 2) which is adjacent tothe ramp lane Wr; and

the lane width of the ramp lane Wr.

In general, the following lane widths have been determined in advance:

the lane width of a driving lane of a highway;

the distance between the outer lane shoulder of the driving lane Wh1 andthe ramp sign; and

the lane width of the ramp lane Wr.

When the condition (2) is satisfied, the own vehicle 50 is running on adriving lane close to the ramp lane Wr. That is, the satisfaction of thecondition (2) allows the ECU 20 as the driving assistance device toeliminate the process of detecting whether or not the own vehicle 50 onthe driving lane Wh2 or the driving lane Wh3 moves to the ramp lane Wr.That is, the satisfaction of the condition (2) can avoid an incorrectdetection of the lane change of the own vehicle 50, as the entry of theown vehicle 50 to the ramp lane Wr, when really the vehicle is changingfrom the driving lane Wh2 to the driving lane Wh1, or from the drivinglane Wh3 to the driving lane Wh2.

The condition (3) detects whether or not the own vehicle 50 is drivingaccording to the instruction of the symbol included in the ramp signsSg1 to Sg4. As shown in FIG. 2, when the own vehicle 50 changes thecurrent driving lane Wh1 toward the right side direction, it is detectedthat the own vehicle 50 has leaved the current driving lane Wh1 andentered the ramp lane Wr on the basis of the instruction of the downarrow symbol Sb included in the ramp signs Sg. In this case, the ownvehicle 50 travels on the basis of the speed limit symbol Sa1 of 90 kmincluded in the ramp sign Sg 1.

On the other hand, as shown in FIG. 2, when the own vehicle 50 changesthe current driving lane Wh1 toward the left side direction, forexample, into the driving lane Wh2, the own vehicle 50 drives withoutfollowing the speed limit symbol Sa1 of 90 km included in the ramp signSg1. In the latter case, the own vehicle 50 can drive without using thespeed limit symbol Sa1 of 90 km included in the ramp sign Sg1.

Because the ramp sign Sg1 is installed at the entrance of the ramp laneWr, the arrangement direction of the ramp sign Sg1 provides anindication of the forwarding direction of the own vehicle 50 towardwhich the own vehicle 50 travels on the ramp lane Wr. Further, as shownin FIG. 2, when the ramp sign Sg1 includes the down arrow symbol Sb asan exit symbol to leave the highway, and the down arrow symbol Sb in theramp sign Sg1 shows the direction to enter the ramp lane Wr, it isacceptable to detect whether or not the travel change direction of theown vehicle 50 is equal to the direction designated by the down arrowsymbol Sb included in the ramp sign Sg1.

The predetermined speed limit of the condition (4) is used to avoidoccurrence of the incorrect detection of determining that the ownvehicle 50 enters the ramp lane Wr when the own vehicle 50 travels on ageneral roadway, not on a highway.

In general, the ramp signs are not installed on general roadways, butinstalled on a ramp lane on highways. However, the conventional drivingassistance device causes an incorrect recognition of detecting that theown vehicle 50 travels on a highway when the own vehicle 50 travels on ageneral roadway. The driving assistance device recognizes a traffic signinstalled on a general roadway as a ramp sign.

The use of the condition (4) suppresses the driving assistance device ofthe ECU 20 from incorrectly determining that the own vehicle 50 isentering a ramp lane Wr. For example, the predetermined speed X isdetermined on the basis of the value of a speed limit used for thedriving lanes Wh1, Wh2 and/or Wh3 on the highway.

The judgment section 26 detects the extent of the ramp lane Wr. That is,because no ramp sign is usually present on general roadways, and on theother hand at least one ramp sign is present on each ramp lane, thejudgment section 26 detects the extent of the ramp lane Wr when one ormore ramp signs are installed along the shoulder of the current drivinglane. As previously described, one or more first type ramp signs and atleast two second type ramp signs are present on a ramp lane. The firsttype ramp sign includes a speed limit symbol and an exit symbol, i.e. adown arrow symbol installed at the entrance of the ramp lane. The secondtype ramp sign includes a speed limit symbol only, not including thedown arrow symbol (exit symbol).

Traffic signs are usually installed on general roadways, highways andramp lanes. Each traffic sign includes a speed limit symbol only and isinstalled along them. However, the speed limit symbols in the ramp signson a ramp lane have a unique arrangement which is different from thearrangement of the speed limit symbols in the traffic signs on drivinglanes of a highway and a general roadway.

In general, at least two or more ramp signs including a speed limitsymbol are installed at relatively narrow intervals along the ramp laneWr so as to provide an indication to quickly reduce the vehicle speed ofthe own vehicle 50. In general, the extent of the ramp lane Wr has ashort distance. The the ramp lane Wr is located between a highway and ageneral roadway, and the own vehicle can leave the highway through theramp lane Wr. The speed limit of each of the speed limit symbols in theramp signs installed along the ramp lane instructs a vehicle toadequately reduce its vehicle speed from the entrance to the exit of theramp lane Wr. These ramp signs including a speed limit symbol only arelocated from the entrance to the exit of the ramp lane Wr in a specificspeed reduction pattern in order to adequately reduce the vehicle speed.For example, a speed limit of each of the ramp signs installed along theramp lane Wr is gradually reduced from the entrance of the ramp lane Wrto the exit from the ramp lane Wr according to the specific reductionpattern of the vehicle speed.

The judgment section 26 judges whether or not the current driving laneis the ramp lane Wr on the basis of the specific arrangement pattern ofthe speed limit symbols included in at least two or more detectedtraffic signs (ramp signs).

That is, the judgment section 26 detects that the extent of the currentdriving lane is equal to the extent of the ramp lane Wr, i.e. the ownvehicle 50 is now running on the ramp lane Wr when the following twoconditions (c1) and (c2) are satisfied after the own vehicle 50 entersthe entrance of the ramp lane Wr:

(c1) the traffic sign detection section 21 detects not less than twotraffic signs, for example, ramp signs Sg1 to Sg4 shown in FIG. 2,arranged along the current driving lane in forward direction of the ownvehicle 50; and

(c2) a speed reduction pattern indicated by speed limit symbols Sa1 toSa4 included in the traffic signs (such as the ramp signs Sg1 to Sg4)detected by the traffic sign detection section 21 in the forwarddirection of the own vehicle 50 satisfies the predetermined speedreduction pattern.

The predetermined distance A is equal to the maximum distance betweentwo traffic signs adjacent to each other, each includes a speed limitsymbol.

When the ECU 20 can receive information of the ramp lane Wr, forexample, transmitted from a vehicle navigation system, etc., it isacceptable to determine the predetermined distance A on the basis of thereceived information regarding the ramp lane Wr.

In addition, the judgment section 26 detects a completion place of theramp lane Wr as the exit of the ramp lane Wr when the speed limit ofeach of the detected traffic signs is reduced according to a patternwhich is different from the predetermined reduction pattern or when thedistance between the adjacent traffic signs is wider than thepredetermined distance A.

For example, it is possible for the judgment section 26 to recognize thetraffic sign located before one traffic sign which does not follow thespecific reduction pattern of the vehicle speed. Further, it is alsopossible for the judgment section 26 to recognize the traffic signincluding the exit symbol, where the distance between the traffic signand another traffic sign positioned further closer is longer than thepredetermined distance A. The judgment section 26 judges that the ramplane Wr has the section from the detected entrance to the determinedcompletion place.

As shown in FIG. 2, the traffic signs (as the ramp signs Sg1 to Sg4) areinstalled along the extent of the ramp lane Wr from the entrance to theexit, and a speed limit value of each of the speed limit symbols Sa1 toSa4 included in the traffic signs Sg1 to Sg4 are reduced from theentrance toward the exit of the ramp lane Wr. The distance D1 betweenthe traffic signs Sg1 and Sg2 is narrow than the predetermined distanceA. The distance D2 between the traffic signs Sg2 and Sg3 is narrow thanthe predetermined distance A. The distance D3 between the traffic signsSg3 and Sg4 is narrow than the predetermined distance A.

The traffic sign detection section 21 does not detect any traffic signat a place within the predetermined distance A outside of the trafficsign Sg4 in the direction toward the exit of the ramp lane Wr. In thiscase, the judgment section 26 detects that the traffic sign Sg4 isinstalled at a place of the exit of the ramp lane Wr.

The judgment section 26 detects that the extent of the ramp lane Wr isfrom the place of the ramp sign Sg1 to the place of the ramp sign Sg4.Usually, a plurality of traffic signs are arranged in the front imagedata in the forward direction of the own vehicle 50. The judgmentsection 26 detects the extent of the ramp lane Wr by using a pluralityof the continuous front image data captured by and transmitted from thein-vehicle camera 10.

When the own vehicle 50 is running along the ramp lane Wr detected bythe judgment section 26, the notification control section 25 notifies,to the driver of the own vehicle 50 through the display unit 31,information regarding the speed limit at the current location of the ownvehicle 50 and that the own vehicle 50 is now running on the ramp laneWr.

FIG. 3A is a view showing the traffic information displayed on thedisplay unit 31. That is, FIG. 3A shows the speed limit symbol of 90 kmand the down arrow symbol Sb as the auxiliary symbol included in theramp sign Sg1 which is installed at the entrance of the ramp lane Wr.

As shown in FIG. 3A, the notification control section 25 transmits tothe display unit 31 the information regarding the 90 km and the downarrow symbol Sb included in the ramp sign Sg1 during the period from thetiming when the lane entry detection section 24 detects entry of the ownvehicle 50 into the ramp lane Wr to the timing when the own vehicle 50has passed through the place of the ramp sign Sg2. When receiving theinformation transmitted from the notification control section 25, thedisplay unit 31 displays the speed limit symbol Sa1 and the down arrowsymbol Sb as the auxiliary symbol included in the ramp sign Sg1.

FIG. 3B is a view showing the traffic information displayed on thedisplay unit 31. That is, FIG. 3B shows the speed limit symbol Sa2 of 70km included in the ramp sign Sg2 and the down arrow symbol Sb as theauxiliary symbol. The ramp sign Sg2 is located at a place forward theramp sign Sg1. The speed limit symbol Sa2 of 70 km included in the rampsign Sg2 and the down arrow symbol Sb are displayed on the display unit31 when the own vehicle 50 is running on the distance D2 between theramp sign Sg2 and the ramp sign Sg3 on the ramp lane Wr.

As shown in FIG. 3B, the notification control section 25 transmits tothe display unit 31 the information regarding the speed limit symbol Sa2of 70 km included in the ramp sign Sg2 and the down arrow symbol Sbduring the period from the timing when the own vehicle 50 passes throughthe place of the ramp sign Sg2 to the timing when the own vehicle 50passes the ramp sign Sg3. When receiving the information transmittedfrom the notification control section 25, the display unit 31 displaysthe speed limit symbol Sa2 of 70 km and the down arrow symbol Sb.

FIG. 3C is a view showing the traffic information displayed on thedisplay unit 31. That is, FIG. 3C shows the speed limit symbol Sg3 of 50km included in the ramp sign Sg3 and the down arrow symbol Sb as theauxiliary symbol. The ramp sign Sg3 is installed at a place before theramp sign Sg2. The speed limit symbol Sa3 of 50 km included in the rampsign Sg3 and the down arrow symbol Sb are displayed on the display unit31 when the own vehicle 50 is running on the distance D3 between theramp sign Sg3 and the ramp sign Sg4 on the ramp lane Wr.

As shown in FIG. 3C, the notification control section 25 transmits tothe display unit 31 information regarding the speed limit symbol Sa3 of50 km included in the ramp sign Sg3 and the down arrow symbol Sb duringthe period from the timing when the own vehicle 50 passes through theplace of the ramp sign Sg3 to the timing when the own vehicle 50 passesthrough the place of the ramp sign Sg4. When receiving the informationtransmitted from the notification control section 25, the display unit31 displays the speed limit symbol Sa3 of 50 km and the down arrowsymbol Sb.

FIG. 3D is a view showing the traffic information displayed on thedisplay unit 31. That is, FIG. 3D shows the speed limit symbol Sg4 of 30km included in the ramp sign Sg4.

As shown in FIG. 3D, the notification control section 25 transmits tothe display unit 31 the information regarding the speed limit symbol Sa4of 30 km only, included in the ramp sign Sg4 after the own vehicle 50has passed through the place of the ramp sign Sg4. When receiving theinformation transmitted from the notification control section 25, thedisplay unit 31 displays the speed limit symbol Sa4 of 30 km only, anddoes not displays the down arrow symbol Sb. This makes it possible forthe driver of the own vehicle 50 to recognize that the own vehicle 50has passed through the exit of the ramp lane Wr.

The driver of the own vehicle 50 often forgets to reduce the vehiclespeed after passing through the entrance of the ramp lane Wr andmaintains a high speed of the own vehicle 50 as if they were on thehighway. As previously described, when the notification control section25 provides the instruction to the display unit 31 to display theinformation regarding the speed limit on the ramp lane Wr, the driver ofthe own vehicle 50 correctly recognizes that the own vehicle 50 isleaving the highway, and entering the ramp lane Wr. That is, theinformation regarding such a speed limit provides to the driver of theown vehicle 50 an indication to reduce the current speed of the ownvehicle 50 to adopt the allowed speed range of the ramp lane Wr.

The display unit 31 (as the notification device) is a meter displayarranged on a vehicle instrument panel, for example. The display unit 31is composed of a liquid crystal display, etc. When the own vehicle 50has a car navigation device, it is possible to use the car navigationdevice as the display unit 31.

A description will now be given of the process of detecting entry of theown vehicle 50 into the ramp lane Wr and notifying the detectedsituation to the driver of the own vehicle 50 with reference to FIG. 4.

FIG. 4 is a flow chart showing the process of detecting a driving stateof the own vehicle 50 on the ramp lane Wr, and notifying the detectedmatter to the driver of the own vehicle 50 through the display unit 31,etc.

The ECU 20 as the driving assistance device according to the exemplaryembodiment performs the process shown in FIG. 4 every time whendetecting whether the own vehicle 50 is entering the ramp lane Wr. Theprocess of detecting the entry of the own vehicle 50 to the ramp lane Wrwill be explained later.

In step S10 shown in FIG. 4, the judgment section 26 in the ECU 20detects a distance of the ramp lane Wr on the basis of the detecteddistances, i.e. the distance between the traffic signs Sg1 and Sg2, thedistance between the traffic signs Sg2 and Sg3, the distance between thetraffic signs Sg3 and Sg4, and the speed reduction pattern. Theoperation flow progresses to step S11.

In step S11, the judgment section 26 judges whether or not the ownvehicle 50 is now running on the ramp lane Wr detected in step S10.

When the result in step S11 indicates affirmation (“YES” in step S11),i.e. indicates that the own vehicle 50 is now running on the ramp laneWr, the operation flow progresses to step S12.

In step S12, the notification control section 25 provides to the driverof the own vehicle 50 information regarding the speed limit and that theown vehicle is now running on the ramp lane Wr through the display unit31. The operation flow returns to step S21.

On the other hand, when the result in step S11 indicates negation (“NO”in step S11), i.e. indicates that the own vehicle 50 is not running onthe ramp lane Wr, the ECU 20 detects that the own vehicle 50 has passedthrough the ramp lane Wr, and completes the execution of the processshown in FIG. 4.

A description will now be given of the process of detecting the entry ofthe own vehicle 50 into the ramp lane Wr with reference to the flowchart shown in FIG. 5.

FIG. 5 is a flow chart showing the process of detecting the entry of theown vehicle 50 into the ramp lane Wr.

The ECU 20 repeatedly performs the process shown in FIG. 5 every timewhen the in-vehicle camera 1 captures front images and transmits thefront image data to the ECU 20 as the driving assistance deviceaccording to the exemplary embodiment.

In step S20, the lane entry detection section 24 judges whether or notthe current vehicle speed of the own vehicle 50 is higher than thepredetermined speed X. That is, the lane entry detection section 24judges whether or not the condition (4) is satisfied. The condition (4)has been previously explained. When the judgment result is step S20indicates negation (“NO” in step S20), i.e. the current vehicle speed ofthe own vehicle 50 is not more than the predetermined speed X, the laneentry detection section 24 judges that the own vehicle 50 has notentered the ramp lane Wr. The ECU 20 completes the process shown in FIG.5.

On the other hand, when the judgment result is step S20 indicatesaffirmation (“YES” in step S20), i.e. the current vehicle speed of theown vehicle 50 is higher than the predetermined speed X, the operationflow progresses to step S21.

In step S21, the lane entry detection section 24 judges whether or notthe traffic sign detection section 21 has detected the presence of aramp sign. That is, the lane entry detection section 24 judges whetheror not the condition (1) is satisfied.

When the judgment result in step S21 indicates negation (“NO” in stepS21), i.e. the traffic sign detection section 21 has not detected anyramp sign, the operation flow progresses to step S25.

In step S25, the lane entry detection section 24 judges that the ownvehicle 50 has not entered into the ramp lane Wr. The ECU 20 completesthe process shown in FIG. 5.

On the other hand, when the judgment result in step S21 indicatesaffirmation (“YES” in step S21), i.e. the traffic sign detection section21 has detected a ramp sign, the operation flow progresses to step S22.

In step S22, the lane entry detection section 24 judges whether or notthe detected distance Le between the own vehicle 50 and the detectedramp sign is smaller than the predetermined distance Y (m). That is, thelane entry detection section 24 judges whether or not the condition (2)previously described is satisfied.

When the judgment result in step S22 indicates negation (“NO” in stepS22), i.e. the distance Le is not less than the predetermined distance Y(m), the operation flow progresses to step S25.

In step S25, the lane entry detection section 24 judges that the ownvehicle 50 has not entered into the ramp lane Wr. The ECU 20 completesthe process shown in FIG. 5.

On the other hand, when the judgment result in step S22 indicatesaffirmation (“YES” in step S22), i.e. the distance Le is narrower thanthe predetermined distance Y (m), the operation flow progresses to stepS23.

In step S23, the lane entry detection section 24 judges whether or notthe arrangement direction of the detected ramp signs in the forwarddirection of the own vehicle 50 is equal to the direction indicated bythe turn signal transmitted from the turn signal indicator unit 11. Thatis, the lane entry detection section 24 judges whether or not thecondition (3) previously described is satisfied.

When the judgment result in step S23 indicates negation (“NO” in stepS23), i.e., the arrangement direction of the detected ramp signs in theforward direction of the own vehicle 50 is not equal to the directionindicated by the turn signal, the operation flow progresses to step S25.

In step S25, the lane entry detection section 24 judges that the ownvehicle 50 has not entered into the ramp lane Wr. The ECU 20 completesthe process shown in FIG. 5.

On the other hand, when the judgment result in step S23 indicatesaffirmation (“YES” in step S23), i.e., the arrangement direction of thedetected ramp signs in the forward direction of the own vehicle 50 isequal to the direction indicated by the turn signal, the operation flowprogresses to step S24.

In step S24, the lane entry detection section 24 judges that the ownvehicle 50 has entered into the ramp lane Wr. The ECU 20 completes theprocess shown in FIG. 5.

The ECU 20 as the driving assistance device according to the exemplaryembodiment has the following effects.

In general, there are installed not less than two traffic signs, i.e.ramp signs including a speed limit symbol at relatively narrow intervalson the ramp lane Wr in the forward direction of the own vehicle 50 onthe ramp lane Wr. The own vehicle 50 can leave a highway through theramp lane Wr. Such a ramp lane Wr has an extent of a short distance toadequately reduce the vehicles peed of the own vehicle 50. Thearrangement pattern of the ramp signs is narrower than that of a drivinglane on a highway and a general roadway. The ramp signs are arranged onthe the ramp lane Wr as a connection lane for the own vehicle 50 toreduce its vehicle speed according to the predetermined speed reductionpattern. Accordingly, it is possible for the ECU 20 as the drivingassistance device according to the exemplary embodiment to detect thepresence of the ramp lane We on the basis of the arrangement pattern ofthe traffic signs (as the ramp signs) and the speed reduction pattern ofthe speed limits included in the detected traffic signs. The trafficsigns installed on a ramp lane are different in arrangement pattern andspeed reduction pattern from traffic signs installed on a driving laneon a highway and a general roadway. Further, the ECU 20 as the drivingassistance device according to the exemplary embodiment can correctlydetect the place of the exit of the ramp lane as the connection lane.

The ECU 20 as the driving assistance device according to the exemplaryembodiment judges with high accuracy that the own vehicle 50 has alreadypassed through the place of exit of the ramp lane Wr when the detectedspeed reduction pattern of the speed limit of each of the detectedtraffic signs is different from the predetermined speed reductionpattern, or when the distance between the adjacent detected trafficpatterns is wider than the predetermined distance A. This makes itpossible to detect the boundaries of the ramp lane Wr with highaccuracy.

During the driving of the own vehicle 50 on the detected ramp lane Wr,the ECU 20 notifies to the driver of the own vehicle 50 the informationregarding the speed limit on the ramp lane Wr and that the own vehicle50 now travel on the ramp lane Wr. This information notifies to thedriver of the own vehicle 50 that the own vehicle 50 is now leaving thedriving lane on the highway, and is an indication to reduce the vehiclespeed. This calls the attention of the driver of the own vehicle 50 tomaintain the vehicle speed within the allowed speed limit of the ramplane Wr.

In general, at least two or more ramp signs including a different speedlimit symbol are installed in the forward direction of the own vehicle50 along the ramp lane Wr in order to adequately reduce the vehiclespeed of the own vehicle 50.

That is, the ECU 20 as the driving assistance device according to theexemplary embodiment detects the presence of a ramp lane, i.e. judgeswhether or not the current driving lane is a ramp lane, and detects thatthe current driving lane is a ramp lane when the following conditionsare satisfied:

a plurality of detected traffic signs include a different speed limitsymbol to each other; and

a speed limit value indicated by each of the speed limit symbols in thedetected traffic signs is reduced in the forward direction of the ownvehicle 50.

Because the ECU 20 can recognize and judge the presence of the the ramplane, it is possible for the ECU 20 as the driving assistance device todetect the exit of the ramp lane and the completion of the driving onthe ramp lane with high accuracy.

In general, a ramp lane is located between a highway and a generalroadway, and the ramp lane is short. The own vehicle 50 can leave thehighway through the ramp lane. When the own vehicle travels on the ramplane, the speed limit value indicated by each of the speed limit symbolsin the detected traffic signs is gradually reduced in the forwarddirection of the own vehicle 50.

According to the speed limit value indicated by each of the speed limitsymbols in the detected ramp signs, the driver of the own vehicle 50 mayreduce the vehicle speed from the entrance to the exit of the extent ofthe ramp lane. This makes it possible to provide safe driving suitablefor the ramp lane.

Usually, an entrance ramp sign is installed at the place of the entranceof a ramp lane Wr. The entrance ramp sign includes a speed limit symboland an exit symbol, for example, a down arrow sign. The own vehicle canleave a highway through the ramp lane and enters a general roadwaythrough the place of the exit of the ramp lane. In particular, noentrance ramp sign is installed on driving lane on highways and generalroadways. The entrance ramp sign is installed on the ramp lane.Accordingly, it is possible for the ECU 20 as the driving assistancedevice to correctly detect the presence of a ramp lane in front of thecurrent driving place of the own vehicle 50 when detecting the entranceramp sign of the ramp lane which includes a combination of the exitsymbol and the speed limit symbol.

Under the condition when the ECU 20 has detected the entrance ramp sign,it is possible for the ECU 20 to judges that the own vehicle 50 nowtravels on a driving lane on a highway, which is located adjacent to thedetected ramp lane, when the distance Le between the entrance ramp signand the own vehicle 50 is narrower than the predetermined distance Y.

Further, when the driver of the own vehicle 50 intends to change the ownvehicle 50 toward the ramp lane, the driver of the own vehicle 50 movesthe own vehicle 50 to the ramp lane from the driving lane Wh1. In thiscase, when the conditions (1), (2) and (3) previously described aresatisfied, the ECU 30 judges that the own vehicle 50 has entered intothe ramp lane Wr. This makes it possible to avoid incorrect detection ofthe entry of the own vehicle 50 into the ramp lane when the own vehicle50 switches the driving lanes on the highway, instead of entering theramp lane. This provides safe driving to the driver of the own vehicle50.

(Various Modifications)

The concept of the driving assistance device (the ECU 20) and thedriving assist method according to the present invention is not limitedby the exemplary embodiment previously described.

For example, the following modifications are also acceptable. It ispossible to perform the drive power control of the own vehicle 50 on thebasis of the detection results regarding the entry of the own vehicle 50into the ramp lane Wr, the completion of this entry, and on the basis ofthe judgment results of detecting the ramp lane Wr. It is acceptable forthe ECU 20 as the driving assistance device to perform a gear shift downcontrol when detecting the entry of the own vehicle 50 into the ramplane Wr.

It is acceptable for the ECU 20 as the driving assistance device todetect the presence of a ramp lane by using traffic signs installedalong the ramp lane, each including an exit symbol and a speed limitsymbol. In other words, even if these ramp signs, each including theexit symbol and the speed limit symbol, are installed along the ramplane Wr, the ECU 20 may detect the extent of the ramp lane on the basisof the arrangement of at least two or more the traffic signs (rampsigns), and a speed reduction pattern indicated by the speed limitsymbols included in the detected traffic signs.

It is acceptable for the ECU 20 as the driving assistance device todetect, as the end place of the ramp lane Wr, the traffic sign at apredetermined number in the detected traffic signs, when the detectedtraffic signs are arranged in a predetermined speed reduction pattern,which is narrower than the predetermined distance. The number of trafficsigns including a speed limit symbol arranged on a ramp lane is usuallyfixed. Because it is sufficient for the ECU 20 to perform the drivingassistance control during a predetermined section in the ramp lane Wr,this control makes it possible to correctly detect the end place of theramp lane Wr.

When a plurality of traffic signs including a speed limit symbol arearranged on the ramp lane Wr, it is acceptable for the ECU 20 as thedriving assistance device to detect, as the end place of the ramp laneWr, a place which is apart from the entrance of the ramp lane Wr by twoor more traffic signs, counted from the entrance of the ramp lane Wr. Ingeneral, because the distance of the ramp lane has been determined, andit is sufficient for the ECU 20 to perform the driving assistancecontrol during the ramp lane Wr having the predetermined distance, it ispossible for the ECU 20 to detect the end place of the ramp lane Wr onthe basis of this condition.

It is possible for the ECU 20 as the driving assistance device to usethe predetermined reduction pattern which contains the same speed limitsas long as the speed limit is reduced from the entrance to the end ofthe ramp lane Wr. For example, it is acceptable for the ECU 20 to usethe speed reduction pattern from the entrance to the exit of the ramplane Wr, which includes 90 km/h, 70 km/h, 70 km/h, 50 km/h and 30 km/h.

It is also acceptable for the ECU 20 to use a plurality of the speedreduction patterns, and detect the ramp lane when the arrangementpattern of the speed limit symbols in the traffic signs is matched withone of the speed reduction patterns.

It is acceptable for the ECU 20 as the driving assistance device todetect the entry of the own vehicle 50 into the ramp lane Wr when theconditions (1), (2) and (3) are satisfied regardless of the state of thecondition (4). That is, it is possible to eliminate step S11 shown inFIG. 4. This modification would cause a possible incorrect detectionregarding the entry of the own vehicle 50 into the ramp lane Wr whencompared with a case of satisfying all of the conditions (1) to (4).However, this modification can also detect entry of the own vehicle 50into the ramp lane Wr.

It is acceptable for the driver's intention detection section 23 in theECU 20 as the driving assistance device to detect the driver's intentionfor the own vehicle 50 to change the current drive lane on the basis ofa steering angle direction of the own vehicle 50 when a steering anglesensor 12 designated by a dotted line shown in FIG. 1 detects a steeringangle and the ECU 20 receives a steering angle signal transmitted fromthe steering angle sensor 12.

Further, it is also acceptable for the driver's intention detectionsection 23 in the ECU 20 as the driving assistance device to detect thedriver's intention for the own vehicle 50 to change the current drivelane on the basis of a yaw rate signal when the yaw rate sensor detectsa yaw rate of the own vehicle 50 and the ECU 20 receives the yaw ratesignal transmitted from the yaw rate sensor 13.

Still further, it is sufficient for the driver's intention detectionsection 23 to detect the driver's intention for the own vehicle 50 tochange the current drive lane on the basis of at least one of theturning instruction signal transmitted from the turn signal indicatorunit 11, the steering angle signal transmitted from the steering anglesensor 12, and the yaw rate signal transmitted from the yaw rate sensor13.

When the own vehicle 50 has a radar unit 14 such as a millimeter-waveradar device designated by a dotted line shown in FIG. 1, it is possibleto measure the distance in a width direction between the own vehicle 50and the ramp lane Sg on the basis of distance information obtained bythe radar unit 14. In this case, it is possible for the distancedetection section 22 to calculate the distance Le between the ownvehicle 50 and the ramp sign Wg on the basis of the distance informationtransmitted from the radar unit 14.

When the own vehicle 50 has a speaker unit 32, as one of thenotification units, designated by a dotted line shown in FIG. 1, it ispossible for the notification control section 25 to notify to the driverof the own vehicle 50 through the speaker unit 32 that the own vehicle50 is now running on a ramp lane and the information regarding the speedlimit of the ramp lane. It is also acceptable for the notificationcontrol section 25 to notify this information to the driver of the ownvehicle 50 through the display unit 31 and the speaker unit 32. It isalso acceptable for the notification control section 25 to notify thisinformation to the driver of the own vehicle 50 through at least one ofthe display unit 31 and the speaker unit 32.

While specific embodiments of the present invention have been describedin detail, it will be appreciated by those skilled in the art thatvarious modifications and alternatives to those details could bedeveloped in light of the overall teachings of the disclosure.Accordingly, the particular arrangements disclosed are meant to beillustrative only and not limited to the scope of the present inventionwhich is to be given the full breadth of the following claims and allequivalents thereof.

What is claimed is:
 1. A driving assistance device comprising: a traffic sign detection section capable of detecting traffic signs including at least a speed limit symbol on a basis of front image data captured by an in-vehicle camera mounted on an own vehicle, a lane entry detection section capable of detecting that the own vehicle is entering a connection lane through which the own vehicle leaves a highway; and a judgment section capable of detecting that a current driving lane, on which the own vehicle travels, is the connection lane when following first and second conditions and are satisfied after the lane entry detection section detects the entry of the own vehicle into the connection lane: (first condition) the traffic sign detection section detects not less than two traffic signs arranged along the current driving lane in a forward direction of the own vehicle, and (second condition) a speed reduction pattern indicated by speed limit symbols included in the traffic signs detected by the traffic sign detection section in the forward direction of the own vehicle satisfy a predetermined speed reduction pattern.
 2. The driving assistance device according to claim 1, wherein the judgment section detects an end place of the connection lane, when the speed reduction pattern indicated by the speed limit symbols included in the traffic sign detected by the traffic sign detection section in the forward direction of the own vehicle is different from the predetermined speed reduction pattern, or when a distance between the detected traffic signs adjacent to each other is wider than a predetermined distance, and the judgment section detects the extent of the connection lane as being from a place of entrance of the connection lane detected by the lane entry detection section to the end place of the connection lane.
 3. The driving assistance device according to claim 1, further comprising: a notification control section capable of notifying, to the driver of the own vehicle through a notification unit, information regarding that the own vehicle now travels on the connection lane and a speed limit value corresponding to the speed limit symbol included in the detected traffic sign at a current location of the own vehicle when the own vehicle travels on the connection lane detected by the judgment section.
 4. The driving assistance device according to claim 2, further comprising: a notification control section capable of notifying, to the driver of the own vehicle through a notification unit, information regarding that the own vehicle now travels on the connection lane and a speed limit value corresponding to the speed limit symbol included in the detected traffic sign at a current location of the own vehicle when the own vehicle travels on the connection lane detected by the judgment section.
 5. The driving assistance device according to claim 1, wherein the judgment section uses the predetermined speed reduction pattern which indicates that the speed limit symbols included in the detected traffic signs have different speed limit values to each other, and being reduced in the forward direction of the own vehicle.
 6. The driving assistance device according to claim 2, wherein the judgment section uses the predetermined speed reduction pattern which indicates that the speed limit symbols included in the detected traffic signs have different speed limit values to each other, and being reduced in the forward direction of the own vehicle.
 7. The driving assistance device according to claim 3, wherein the judgment section uses the predetermined speed reduction pattern which indicates that the speed limit symbols included in the detected traffic signs have different speed limit values to each other, and being reduced in the forward direction of the own vehicle.
 8. The driving assistance device according to claim 4, wherein the judgment section uses the predetermined speed reduction pattern which indicates that the speed limit symbols included in the detected traffic signs have different speed limit values to each other, and being reduced in the forward direction of the own vehicle.
 9. The driving assistance device according to claim 1, further comprising: a distance detection section capable of detecting a distance in a width direction of the own vehicle between the own vehicle and the detected traffic sign, which includes an exit symbol and the speed limit symbol, the exit symbol providing for the own vehicle to leave the highway and enter the connection lane; and a driver's intention detection section capable of detecting a driver's intention for the own vehicle to change the current driving lane, wherein the lane entry detection section detects that the own vehicle has entered the connection lane when: the traffic sign detection section has detected the traffic sign including the exit symbol and the speed limit symbol; the distance detected by the distance detection section is narrower than a predetermined distance; and the direction of the own vehicle when changing the current driving lane detected by the driver's intention detection section is equal to the direction of the traffic sign including the exit symbol and the speed limit symbol.
 10. The driving assistance device according to claim 2, further comprising: a distance detection section capable of detecting a distance in a width direction of the own vehicle between the own vehicle and the detected traffic sign, which includes an exit symbol and the speed limit symbol, the exit symbol providing for the own vehicle to leave the highway and enter the connection lane; and a driver's intention detection section capable of detecting a driver's intention for the own vehicle to change the current driving lane, wherein the lane entry detection section detects that the own vehicle has entered the connection lane when: the traffic sign detection section has detected the traffic sign including the exit symbol and the speed limit symbol; the distance detected by the distance detection section is narrower than a predetermined distance; and the direction of the own vehicle when changing the current driving lane detected by the driver's intention detection section is equal to the direction of the traffic sign including the exit symbol and the speed limit symbol.
 11. The driving assistance device according to claim 3, further comprising: a distance detection section capable of detecting a distance in a width direction of the own vehicle between the own vehicle and the detected traffic sign, which includes an exit symbol and the speed limit symbol, the exit symbol providing for the own vehicle to leave the highway and enter the connection lane; and a driver's intention detection section capable of detecting a driver's intention for the own vehicle to change the current driving lane, wherein the lane entry detection section detects that the own vehicle has entered the connection lane when: the traffic sign detection section has detected the traffic sign including the exit symbol and the speed limit symbol; the distance detected by the distance detection section is narrower than a predetermined distance; and the direction of the own vehicle when changing the current driving lane detected by the driver's intention detection section is equal to the direction of the traffic sign including the exit symbol and the speed limit symbol.
 12. The driving assistance device according to claim 4, further comprising: a distance detection section capable of detecting a distance in a width direction of the own vehicle between the own vehicle and the detected traffic sign, which includes an exit symbol and the speed limit symbol, the exit symbol providing for the own vehicle to leave the highway and enter the connection lane; and a driver's intention detection section capable of detecting a driver's intention for the own vehicle to change the current driving lane, wherein the lane entry detection section detects that the own vehicle has entered the connection lane when: the traffic sign detection section has detected the traffic sign including the exit symbol and the speed limit symbol; the distance detected by the distance detection section is narrower than a predetermined distance; and the direction of the own vehicle when changing the current driving lane detected by the driver's intention detection section is equal to the direction of the traffic sign including the exit symbol and the speed limit symbol.
 13. A driving assistance method performed by a driving assistance device mounted on an own vehicle, comprising steps of: detecting traffic signs including a speed limit symbol on a basis of front image data captured by an in-vehicle camera mounted on an own vehicle; detecting that the own vehicle enters a connection lane, through which the own vehicle leaves a highway; and detecting that a current driving lane, on which the own vehicle travels, is the connection lane as a ramp lane when following first and second conditions and are satisfied after the lane entry detection section detects the entry of the own vehicle into the connection lane: (first condition) not less than two traffic signs arranged along the current driving lane in forward direction of the own vehicle are detected; and (second condition) an arrangement of speed limit symbols included in the detected traffic signs in the forward direction of the own vehicle satisfy a predetermined speed reduction pattern. 